Several examples of homogeneous olefin polymerization catalysts appear in the literature for a variety of transition (W. Kaminsky & R. Steiger in Polyhedron, 1988, vol. 7, no. 22/23, pp. 2375-2381), lanthanide (P. L. Watson in J. Am. Chem. Soc., 1982, vol. 104, no. 1, pp. 337-339) and actinide (P. J. Toscano and T. J. Marks in J. Am. Chem. Soc., 1985, vol. 107, no. 3, pp 653-659) metal complexes. Most of the homogeneous olefin polymerization catalysts reported to date require the use of a soluble cocatalyst such as methylaluminoxanes (MAO). One particular advantage of the homogeneous catalysts is the absence of corrosive components in the formulation and reduction of the number of components required to prepare them, as compared to a typical heterogeneous catalyst. Several disadvantages limit the utility of this method of catalysis in industrial olefin polymerization processes. These include the expense of MAO due to the extremely high ratios of MAO frequently needed to efficiently polymerize olefins, batch to batch variation of the MAO and generally low molecular weight products are obtained which have limited application.
R. F. Jordan in J. Chem. Ed., 1988, vol. 65, no.4, pp 285-289 discloses another form of homogeneous olefin polymerization which includes cationic polymerization catalysts. These polymerization catalysts generally produce polymers with narrow molecular weight distributions and high molecular weights. They generally contain a transition metal component such as titanium or zirconium with a cyclopentadienyl group or other cyclodienyl group and a cation prepared from the reaction with a salt. The complexes are generally very air sensitive and require special handling. The polymerization reaction is very solvent dependent and generally requires solvents, such as methylene chloride, diethyl ether and tetrahydrofuran, not typically used in the industrial preparation of ethylene polymers.
Complexes of the general type LTiX.sub.3 have been disclosed by R. E. Campbell and J. G. Hefner in U.S. patent application Ser. No. 07/462,861, filed Jan. 5, 1990, now U.S. Pat. No. 5,045,517 for the preparation of syndiotactic polystyrene where L is a n-bonded group such as cyclopentadienyl or indenyl and X is an alcohol, halide or amide. A cocatalyst is required for the polymerization reaction such as MAO (methylaluminoxane) in a range of Al:Ti atomic ratio of from about 50:1 to about 10.000:1. For any polymerization reaction it is highly desirable to eliminate or reduce the amount of MAO required as it is expensive and difficult to produce with consistency.
D. F. Birkelbach in U.S. Pat. No. 4,120,820 and U.S. Pat. No. 4,189,553 has also disclosed a more complex mixture for the polymerization of olefins utilizing Ti complexes of the general formula LTiX.sub.3 in which X is a halide and L is an electron donor. The nature of the L group does not describe specifically a n-donor as used in this art. Furthermore, this mixture required components such as a dialkyl magnesium and an alkylaluminum or an alkylaluminum halide in order to produce an active catalyst.
It would be desirable to have available a catalyst with a reduced number of components required to produce an active catalyst for the polymerization of .alpha.-olefins.